Contamination of food with foreign substances and food poisoning are some of major social problems. The term HACCP has recently become familiar to even general consumers. The principal of HACCP is total management for safety and health in (food) manufacturing processes. The comprehensive countermeasures including designs of plants, manufacturing equipment and devices, and delivery are required for the total management. There is a manufacturing standard called GMP (Good Manufacturing Practice) for improvement in manufacturing environments and health to effectively prevent contamination of the manufacturing environments with offending substances. Compliance with the GMP standard to achieve the goals of the HACCP plans has been highly demanded. The GMP standard mainly focuses safety management of employees and plants and process management, but also has a requirement that machines and equipment are to be ‘designed adequately for cleaning’. In food industries, there are various measures to ensure safety handling of particulate materials and prevent contamination with foreign substances in particulate supply equipment.
The foreign substances as potential contamination of the particulate products include metal pieces, glass pieces, gravels, plastic pieces, hairs, wood pieces, paper pieces, little pieces of thread, and rubber pieces. These foreign substances may be mixed both in a material supply process as those present in a row material and in a manufacturing step. These foreign materials may be mixed also in a manufacturing step.
Various particulate supply systems are used in food plants according to their scales, ranging, for example, from manual feed into blenders and other processing devices in small plants, to auto bag-opening and to auto measurement and auto particulate supplies from silos in big plants. There are accordingly diverse process steps in the food plants, for example, a stock process, a measurement process, an auto bag-opening process, a manual feed process, a pneumatic conveying process, a foreign substance removal process, and a dust elimination process. The manual feed process has a high potential for contamination with foreign substances in the manufacturing area required to have strict cleanness. Such facilities are to be improved promptly also from the viewpoint of the workers' safety.
In the pneumatic conveying system, zoning is allowed between a particulate supply area and a food production area. A sifter or magnets located between the two areas can be used to remove foreign substances or insect pests mixed in particulate materials. Additionally, one batch of the particulate material can be kept for the next process and thus the working efficiency can be improved by using a dumping server (manual-feed pneumatic conveying device) or a pneumatic conveying receiver also as a storage bin.
There are possibilities of ‘exterior contamination with foreign substances’ and ‘interior generation of foreign substances’ in the devices of the respective process steps, and various countermeasures have been proposed.
In order to prevent ‘exterior contamination with foreign substances’, the whole line should be designed to be full-automatic and fully closed. If this is not practical, strict zoning tactics should be adopted to prevent contamination with foreign substances.
It is often assumed that the particulates are dry and are thus not suitable for propagation of microorganisms even if the particulates are food. Under certain conditions, however, dew condensation may occur in the line (especially in the stock step) to cause propagation of microorganisms and trigger ‘interior generation of foreign substances’. The aggregates and lumps of particulates may breed insect pest. The possible countermeasures against this problem are ‘thorough cleaning of parts with a high potential for adhesion of particulates to make a dead stock’, ‘adequate design and selection of devices with little potential for adhesion and accumulation of particulates’, and ‘minimized dew condensation due to a temperature difference in devices’.
Cylindrical sifters are generally used to prevent contamination with foreign substances and to remove and crush aggregates and lumps of particulates. The cylindrical sifters include inline sifters (see, for example, WO 02/38290A1 and Japanese Patent Laid-Open Gazette No. H-6-321335) and non-inline sifters (see, for example, Japanese Patent Laid-Open Gazette No. H-3-131372, No. H-11-244784, No. S-63-69577, No. H-6-303, and No. S-57-12278). Recently developed have been high-performance sifters that have blades on a shaft rotating at a high speed in a cylindrical sieve for forcible sieving.
Diverse cylindrical sieves have been developed to be adopted in such cylindrical sifters.
[Patent Document 1] Japanese Utility Model Laid-Open Gazette No. S-60-95986
This invention provides a sieve mounting structure adopted in a cylindrical sifter 1. A mounting frame 2, to which sieves 3 and 21 are mounted, is formed in a substantially cylindrical shape and includes two circular end frames 5 located on both ends in a bus direction S and a linkage frame 7 extended in the bus direction S for linkage of the two end frames 5. The sieves 3 and 21 have lock elements 9 and 22 provided on both ends thereof in the bus direction S. A large number of through holes 10 and 28 are made between the lock elements 9 and 22. The lock elements 9 and 22 of the sieves 3 and 21 are attached to the end frames 5 by means of fixing elements 4 and 23. The sieves 3 and 21 are strained in the bus direction S inside the mounting frame 2. The mounting frame 2 also includes intermediate frames 6 and 25 that are located between the end frames 5 and are joined with the end frames 5 via the linkage frame 7. The lock elements 9 and 22 of the sieves 3 and 21 are mounted on the intermediate frames 6 and 25 via the fixing elements 4 and 23. The intermediate frames 6 and 25 have a smaller diameter than the diameter of the end frames 5 and are gradually tapered. Rubber cushions 14 are interposed between the sieves 3 and 21 and the intermediate frames 6 and 25.
In this prior art structure, the sieves 3 and 21 are attached with tension to the end frames 5 of the mounting frame 2 by means of the fixing elements 4 and 23 having screws, washers, and nuts. This structure lessens the number of attachments and facilitates the mounting operation. The most areas of the sieves 3 and 21 except the areas close to the lock elements 9 and 22 and the seams exert the sieving function and have practically smooth surface. This ensures the smooth flow of object particulates to be processed without causing localized abrasion. Tension of the strained attachment prevents slacks and thus prevents clogging of the sieves having even low rigidity, making the processed particulates flow smoothly.
The prior art structure disclosed in Patent Document 1, however, still has some drawbacks as discussed below:
(1) The sieves 3 and 21 are fastened to the end frames 5 of the mounting frame 2 by the fixing elements 4 and 23 and are strained through adjustment of the screws. It is practically impossible to set the perfectly even clamping force of the fixing elements over the cylindrical faces of the sieves. There is naturally a variation in tension over the faces of the sieves 3 and 21. The varying tension may cause slacks of the sieves 3 and 21. For example, the areas close to the screws may be tightly strained, while the residual areas may be rather loose. The local clamping of the sieves 3 and 21 with the fixing elements may deform the sieves 3 and 21 to have wavy edges. Namely only skilled workers can successfully strain the sieves to set relatively even tensions over the sieves, whereas unskilled workers may have a failure and time-consuming post-adjustment may be required).
There are high-performance cylindrical inline sifters that have blades on a shaft rotating at a high speed in the sieve for forcible sieving. The slacks of the sieves 3 and 21 may cause the rotating blades to come into contact with and damage the sieves 3 and 21.
(2) Attachment and detachment of the screws of the fixing elements 4 and 23 are rather time-consuming and make replacement of the sieves 3 and 21 troublesome. Fixation of the sieves 3 and 21 having the larger diameter by the fixing elements 4 and 23 is often beyond one worker's control.
By taking into account the drawbacks of the prior art structure discussed above, the cylindrical sieve of the invention aims to enable even an unskilled worker to easily equalize the tension over the sieve by simple operations without causing any slack and to enable only one worker to easily replace even a large net member.